Phase noise, caused by oscillator imperfections, affects the orthogonality of subcarriers in an orthogonal frequency-division multiplexing (OFDM) system. The phase noise process may be random in nature and for a phase-locked loop (PLL) based oscillator, it effectively causes a rotation of time domain baseband samples of the in-phase and quadrature components (IQ samples) by a small amount, and the randomness can be characterized by a power spectral density (PSD) in the frequency domain. This leads to a common phase error (CPE), which has similar impact on each subcarrier, and inter-carrier interference (ICI), which may be different for each subcarrier and may cause scattering of the received constellation points in OFDM based systems. The total power of CPE and ICI observed at the center tone may be the integrated phase noise PN (IPN), which may also be obtained by integrating the PSD of the PN process over the occupied bandwidth (BW). If the phase noise PSD is wide compared to the subcarrier spacing, more of the total power of the phase noise (IPN) will be contributed as ICI instead of as CPE. The phase noise may be particularly severe for higher carrier frequencies such as millimeter-wave frequency bands above 6 GHz.
A phase tracking reference signal (PTRS) has been introduced in the New Radio (NR) standard, to enable compensation of oscillator phase noise. PTRS may be utilized at high carrier frequencies (such as millimeter-wave) to mitigate phase noise. However, a fully distributed PTRS structure may be suitable only for CPE estimation and compensation, and may not be of use in mitigating ICI.